The present invention relates generally to hydrodynamic bearings. More particularly, the present invention relates to a method, and associated apparatus, for applying a fluid lubricant to a hydrodynamic bearing.
The fluid lubricant is applied to the bearing to fill clearance spaces separating moving parts of the bearing. When fluid lubricant is applied to the bearing to fill the clearance spaces according to the teachings of the present invention, problems associated with pockets of trapped air in the bearing are minimized. In particular, pockets of air trapped in the bearing during application of the fluid lubricant to the bearing are collapsed, and thermally-related expansion of the pockets of air, once collapsed, does not present problems during operation of the bearing.
Many types of bearings and bearing assemblies are commercially available for use in many different types of devices. Conventional radial bearings and conventional ball bearings are examples of types of bearings which are commercially available and widely utilized.
A disk drive assembly is exemplary of a device which utilizes bearings. A disk drive assembly is a computer mass storage device from which data may be read and/or to which such data may be written. Generally, a disk drive assembly includes one or more randomly-accessible rotating storage media, or disks, on which the data is encoded. An inner diameter of the disk is affixed to a hub which is rotationally coupled to a stationary spindle shaft by a pair of bearings, conventionally ball bearings. The pair of bearings is typically formed of an upper bearing and a lower bearing.
As disk drive assemblies increasingly are constructed to be of reduced heights, the length of the spindle shaft and the spacing between the upper and lower bearings must be reduced. That is to say, as the height of the disk drive assembly is reduced, a proportionately shorter spindle shaft must be accommodated within the disk drive assembly of the reduced height. As a shorter spindle shaft is required, the spacing between the bearings must correspondingly be reduced.
As the upper and lower ball bearings must be spaced apart by shorter distances and the concomitant trend towards smaller nonrepetitive runout (NRRO) and higher spin rates, continued use of conventional ball bearings increasingly becomes a problem. In particular, shorter spacing between the bearings results in reduced tilt stiffness and a reduced rocking mode frequency, either of which, if severe, can cause drive failure of the disk drive assembly. Additionally, lubricant film thicknesses associated with ball bearings are inherently very thin and little attenuation of surface defects and imperfections in the ball bearings is provided by the thin lubricant film. Large amounts of repetitive runout or repetitive path deviation traced out by the spin axis of the spindle bearing can result. Such runout and path deviation, if severe, can also cause damage to the disk drive assembly.
The aforementioned U.S. Pat. Nos. 4,795,275; 5,067,528, and 5,112,142 all disclose a hydrodynamic bearing. While not so limited, bearings similar to the bearings disclosed therein are of particular utility in overcoming the inherent disadvantages of conventional ball bearing-supported spindles utilized in a disk drive assembly.
The hydrodynamic bearing includes a lubricant film of a fluid lubricant applied to clearance spaces formed between sliding metal surfaces of the bearing. The lubricant film provides a high degree of viscous damping and, when used in substitution for conventional ball bearings in a disk drive assembly, permits increased tracking performance to be achieved by the disk drive assembly. Increased tracking performance is advantageous as increased drive track densities of a disk and, hence, increased storage capacities of a disk are permitted. Additionally, the lubricant film further serves to dampen external shock and vibration.
Typically, once a hydrodynamic bearing is assembled, a lubricant is then applied to fill the clearance spaces separating moving parts of the bearing. During application of the lubricant, pockets of air or other gasses existent in the bearing can become trapped in the bearing. For purposes of simplicity, the term "air" shall herein refer to any gaseous media. During operation of the bearing, heat is generated, and the thermal expansive properties of the air pockets cause the volumetric dimensions of the air pockets to increase responsive to the heat generation. Such increased volumetric dimensions of the air pockets can cause the lubricant to be pushed out of the bearing as a result of expansion of the air pockets. Therefore, care must be exercised to minimize the trapping of pockets of air in the bearing during application of the lubricant to the bearing.
It is with respect to these considerations and other background information relative to hydrodynamic bearings that the significant improvements of the present invention have evolved.